RES Technical Corner by Joshua Doores, Colliers Engineering & Design

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Technical Corner

by Joshua Doores, Electrical Engineer, Colliers Engineering & Design

For the article this month, I will be highlighting Article 625 from the 2017 NEC which provides guidance on ‘Electrical Vehicle Charging Systems’. The entire article is broken into (4) sections; General, Equipment Construction, Installation, and Wireless Power Transfer Equipment.

SECTION I - GENERAL provides important definitions that help to clarify the various parts of the Electric Vehicle Charging System. Refer to the final page in this article for an illustration showing the different parts of Electric Vehicle Supply Equipment (EVSE). While not specifically defined in Article 625, electric vehicle charging stations are commonly categorized into 3 categories; Level I, Level II, and DC Fast Charging. Level 1 – Operates on 120VAC, 20A circuit; is almost always a cord and plug connection type and provides 1.2kW – 1.7kW of power. A full 100-mile charge can take 20-24 hours of charging. Level 2 – Operates on 208-240VAC, 40A-60A branch circuit; can be either cord and plug or hard-wired and provides 6.2kW – 10.2kW of power. A full 100-mile charge can take 3-5 hours of charging. DC Fast Chargers - Typically operate at 480VAC, 3ph. There is a large range of power options available ranging from 50kW to 350kW. A full 100-mile charge can take a little as 30mins with a DC Fast Charger.

SECTION II – EQUIPMENT CONSTRUCTION is most important if you are a manufacturer of EVSE components. The following sections I found to be important from the standpoint of an applications engineer.

625.15 – Markings

Any equipment being used for electric vehicle charging must be marked as such, that would include receptacle enclosures, disconnect switches, the charging station itself. The NEC utilizes the verbiage ‘FOR USE WITH ELECTRIC VEHICLES’. The other important marking refers to section 625.52 which discusses whether ventilation is required or not. Depending on the specific circumstance, marking ventilation as 'NOT REQUIRED' or 'VENTILATION REQUIRED' may be required.

625.17(A)(3) and (C) – Cords and Cables

This section discusses the supply and output cable types, ampacity, and lengths. The types and ampacity should come with the unit as a package, however if that is not the case, you will want to reference Table 400.4 and look for Electric Vehicle Cable. EV chargers are considered continuous loads and so equipment should be rated for 125% the full load. Sections (A)(3) and (C) specifically discuss the length of cable allowed. For cord and plug connected EVSE, the code requires an interrupting device inside or within 12in of the attachment plug. Therefore, if the interrupting device is located inside the supply controller, then the supply cord shall be no longer than 12in, if the interrupting device is inside the plug or within the cable, 12in from the plug, the supply cable must be 6ft-15ft long. All of this should come from the factory meeting code if the product is UL listed. Section (C) discusses the overall cable length, which is defined as the cable length from the power supply attachment plug to the output cable connector. This maximum length shall be 25ft unless a listed cable management system is part of the EVSE. Therefore, if you had a 10ft supply cord, the maximum output cable length is 15ft. If you wanted a longer output cable, there must be a cable management system. If your supply controller is fixed in place and power is hard-wired to the unit, then you have all 25 of the allowable feet available for the output cable.

625.18 – Interlock

An interlock shall be provided with the EVSE such that the connector is de-energized whenever it is uncoupled from the electric vehicle. NOTE: This is not required for portable cord and plug connected EVSE intended for connection to receptacles rated 125V, single phase, 15A or 20A. So essentially, residential level 1 charger systems that are cord and plug may not have this interlocking feature.

625.19 – Automatic De-Energization of Cable

A method of sensing cable strain and/or rupture and then automatically de-energizing the output cable and connector is required to prevent exposing users to live electric components inside the cable and/or connector. NOTE: This is not required for portable cord and plug connected EVSE intended for connection to receptacles rated 125V, single phase, 15A or 20A. So essentially, residential level 1 charger systems that are cord and plug may not have this strain sensing feature.

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625.22 Personnel Protection System

The EVSE shall have a listed system of protection against electric shock of personnel. If a cord and plug is used for power supply, an integral interrupting device at the plug or within 12in of plug is required. 625.54 requires the use of GFCI receptacles rated 150V to ground or less and 50A or less. If hard wiring a charger and the branch circuit is 150V line to ground or less and 50A or less, I would recommend a GFCI breaker be used.

SECTION III - INSTALLATION

This is the most important section for the applications engineer who will be designing the installation of an EV charger.

625.40 – EV Branch Circuit

Each outlet installed for the purpose of charging electric vehicles shall be supplied by an individual branch circuit. I wouldn’t even put a maintenance receptacle on the same branch as the EV charger branch. If there are 5 EV chargers, then one must provide (5) branch circuits.

625.41 Overcurrent Protection

Electric Vehicle Charger branch and feeder circuits shall be sized for continuous operation and therefore overcurrent protection shall be rated for not less than 125% of the maximum load.

625.43 Disconnecting Means

Required for EV equipment rated more than 60A or more than 150V line to ground. Disconnecting means shall be installed in a readily accessible location and shall be lockable open in accordance with 110.25. This requirement starts to come into play with larger level 2 commercial chargers and DC fast chargers rated 480V, 3ph.

625.44(A-C)

Provides acceptable receptacle types for portable, stationary, and fixed equipment. Fixed equipment requires a hard-wired connection.

625.46 Loss of Primary Source

Upon loss of voltage from utility or other power systems, energy cannot be back fed through the electric vehicle unless permitted by 625.48.

625.48 Interactive Systems

EVSE that is part of an interactive system that serves as optional standby power shall be listed, evaluated for use with specific EV, and marked suitable for that purpose.

In that case, the requirements of Article 702 shall apply. This is a very interesting aspect of EV charging that requires more research on my part and could probably serve as a source of an article on its own.

625.50 Location

The coupling means (EV connector) of the EV Charger shall be stored and/or located at least 18in above the ground for indoor applications and 24in above ground for outdoor applications.

625.52 Ventilation

Ventilation is only required in indoor charging applications with vehicles that have batteries listed as needing ventilation. Therefore, the only time ventilation is done is if you knew that you were going to be charging vehicles indoors that have batteries that need ventilation. Because of this, it is almost never done. Currently, the vast majority of batteries being used in EV’s do not require ventilation. That being said, if you were going to include a ventilation system, if would have to meet the following requirements:  Mechanical ventilation shall be required for both supply and exhaust air directly from the outdoors.

For ventilation volume requirements, refer to Table 625.52(B)(1)(A)  The supply circuit to mechanical ventilation equipment shall be electrically interlocked with the

EVSE and shall remain energized during the entire charging cycle.  Equipment shall be marked in accordance with 625.15  Equipment receptacles shall be rated and marked and shall be switched such that the ventilation system shall be electrically interlocked through the switch supply power to the receptacle.

625.54 GFCI Protection for Personnel

All single-phase receptacles installed for connection of electric vehicle charging that are rated 150V to ground or less, and 50 amperes or less shall have GFCI protection for personnel.

The final section is devoted to the Wireless Power Transfer Equipment Technology. This type of charging involves a base plate, a charger power converter, and a cable connecting the 2. The EV sits on top of the base plate and is charged in a wireless manner. This is not as popular a technology at the moment, but something to be aware of.

Another charging technology that is being developed is the idea of using battery powered charger stations and utilizing solar panels in conjunction with the battery powered system. This technology was not talked about in Article 625 of the 2017 code but could be included in future editions.

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1.) Supply Controller & Human Interface: This is the brains of the operation. Grid power is input to the controller either via hardwiring or via an approved receptacle. And power to the electric vehicle is transferred via the output cable and connector.

2.) Supply Power Cable: Cord and plug assembly rated for the supply controller and designed to interface with an approved dedicated receptacle. Connects the supply controller to utility power.

3.) GFCI/Weatherproof Receptacle: An approved connection and disconnection means where it meets the requirements of 625.44

in use, and a protected raceway for hardwiring the controller. 4.) EV Charger Receptacle: The pedestal provides many benefits to the EV system, primarily allowing for the supply controller to be mounted without the need for a wall, a place to store the output cables and connectors while not

5.) Branch Circuit Conduit and Conductors: Whether a receptacle and power supply cable are used or if the controller is hard-wired, power from a local panel board will be required to be run out to the EV charger.

6.) Output Cable to Electric Vehicle: Cable used to connect the supply controller to the electric vehicle via the connector and coupling system. Length of cable is limited to 25ft. unless equipped with a cable management system.

7.) Electric Vehicle Connector: The plug end on the output cable. There is a different connector for AC charging (Levels 1 & 2) versus DC Fast Charging. There are also different connectors depending on which part of the world you are in (similar to how there are different receptacle plug types depending on where you are in the world). The US has standardized around the J1772 Type Connector.

res - technical corner Hopefully this article finds you well and can be used as a reference for your project needs.If anyone would like to contribute to the Rochester Engineer and add an article or would like to request information on a specific topic (not limited to Electrical) just email Brett Eliasz at beliasz@bergmannpc.com. As always, any comments are appreciated! Thank you for reading.

Brett Eliasz, P.E., LEED AP BD+C , RES Director Joshua Doores, Electrical Engineer

Colliers Engineering & Design

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